1. Field of the Invention
The present invention relates to a pressure reducing valve, in which the maximum outlet pressure can be safely set.
2. Description of the Related Art
Generally, when a pressurized fluid is supplied from a fluid pressure source to a fluid pressure apparatus at a desired pressure, a pressure reducing valve is interposed therebetween. The pressure reducing valve reduces the primary pressure of the fluid pressure source into a downstream pressure as desired by the fluid pressure apparatus connected thereto.
FIG. 1 shows a conventional pressure reducing valve, which basically includes a valve seat 30 and a valve disk 32 in a body 8 in which a inlet port 4 and an outlet port 6 are defined. The valve disk 32 is urged upwardly to the valve seat 30 by a valve spring 36. When the valve disk 32 is forced to move downwardly, the fluid flows from the inlet port 4 into the outlet port 6, through a gap formed between the valve disk 32 and seat 30.
The upper portion of the valve disk 32 is normally pressed downwardly by a spring 24, via a diaphragm 22. A downward force of the spring 24 can be adjusted by a nut 20 which is displaceable in the directions shown by arrows X-Y, by rotating a screw member 16 fixed to a knob 18. The fluid pressure in the outlet port 6 is determined so that an upward force exerted by the fluid pressure in the outlet port 6 onto the diaphragm 22 is brought to a balance against the downward force of the spring 24.
In the conventional pressure reducing valve shown in FIG. 1, however, there arises a danger of over-pressing the spring 24, until the windings of the spring come to contact with each other remaining a zero winding pitch, since the displacement of the nut 20 is not posed any limit. When over-pressed, the spring 24 cannot be pushed back by the diaphragm 22, and the valve disk 32 is kept apart from the valve seat 30 at a position in the direction shown by the arrow X. As a result, there has been a problem that the primary pressure of the fluid pressure source without being reduced is applied to the fluid pressure apparatus connected downstream the pressure reducing valve and damage it.
To cope with this problem, a stopper for the nut 20 may be provided at the end of the screw member 16. However, with such a fixed stopper, the maximum set pressure of the pressure reducing valve is fixed at a value that would make it difficult to adapt to the operating pressure range of the downstream fluid pressure apparatus.
Besides, the maximum set pressure determined by the fixed stopper may be affected by dimensional errors of components, an error in the spring modulus, etc, of the pressure reducing valve, which cause the maximum set pressure to deviate from a target pressure.